Industry experts are increasingly concerned that the continued furious pace of housing sales is becoming a giant bubble about to burst.

If the bubble does burst, it would be especially painful in New York.

“There have been symptoms of bubble-like behavior in certain regions like Boston, New York and California,” said Dick Hoey, chief economist at Dreyfus. “In certain regions, including New York, housing prices are not falling into the government’s affordability ratio – meaning the person with the median income can’t afford the house with the median price.”

With Wall Street firms paring employees, interest rates likely to rise in the 18 months, continued terrorist threats and stubborn economic weakness, some worry the bubble in New York won’t stay inflated much longer.

Yesterday, the National Association of Realtors said sales of previously owned homes increased 4.5 percent last month to an annual rate of 5.33 million, which would be a record.

The Commerce Department said new-home sales rose 6.7 percent to a record 1.017 million pace.

Prices are up, on average, 7.3 percent from a year ago on a nationwide basis, though New York prices have spurted up much more.

“I do believe there’s a housing bubble in New York,” said Nancy Frank, a Manhattan-based financial planner, who recently advised her clients, a married couple who are uncertain of their long-term employment because they both work on Wall Street, not to buy an mansion in Westchester.

But Frank is aware that many other New Yorkers are not heeding her advice.

“Welcome to the world of the $1 million one-bedroom,” she said. “I don’t know who’s buying them, but they are selling, especially on the Upper East Side.

“Oddly enough, some people are buying real estate now because they think that’s a safer place to be than in the stock market. But they have to realize that they are buying high. It’s true that the movement of real estate prices usually lags the movement of stock prices.”

In 1987, the stock market crashed, but the real estate market didn’t follow until 1991.

The current stock market sell-off started in early 2000, and housing prices have not yet started to fall.

But economists have identified five pins that could prick the real estate bubble:

* A double-dip recession, a distinct possibility for the U.S. economy, could be one pin.

* A hike in interest rates, unlikely in the short term but highly probable sometime next year. Most economists believe much of the current strength of the housing market can be attributed to low mortgage rates.

That’s what’s taken some of the steam out of Boston’s rapidly forming real estate bubble.

“When Putnam announced big layoffs and Fidelity followed up with a big cost-cutting initiative, Boston’s real estate brokers started quaking in their boots,” said John Benanzio, editor of Fidelity Insight, a newsletter that tracks the mutual fund giant. “Boston real estate is so dependent on the health of the big asset management companies.”

Likewise, New York’s real estate market is highly correlated to the health of Wall Street, where many firms are said to be preparing more job cuts.

There are also concerns, rarely expressed in public by real estate brokers, that another terrorist attack, especially a “dirty bomb” quickly would sink the New York housing market.

BUBBLE TROUBLE

Fueled by low mortgage rates, sales of previously owned homes jumped 4.5 percent last month, while new-home sales surged 6.7 percent. But exuberence over housing could be yet another market bubble, in danger of being popped by a variety of forces: